Squirrel-cage rotor for an asynchronous induction motor

ABSTRACT

The novel squirrel-cage rotor should enable a power output of the motor of more than 1 MW even at rotation speeds of more than 10,000 rpm. To this end, the conductor bars ( 4 ) of the squirrel cage are soldered into slots ( 8, 9 ) arranged on the periphery of the massive rotor core ( 3 ) across their entire length, and the conductor bars are arranged to be flush with the surface ( 13 ) of the rotor core ( 3 ).

BACKGROUND OF THE INVENTION

The invention relates to the field of dynamoelectric machines and isapplicable for the constructive configuration of the rotor of anasynchronous induction motor which has windings configured as conductorbars and short-circuited by end rings.

A conventional asynchronous machine of this type has a rotor core ofmassive steel whereby the rotor surface facing the air gap is formedwith slots which have slot walls respectively converging outwardly inradial direction. The winding associated to the rotor is configured assquirrel-cage winding and is made of metallic conductor bars which arearranged form-fittingly in the rotor slots. The portions of the metallicconductor bars, disposed outside the laminated core of the stator, formtogether an assembled ring-shaped winding part, whereby these portionsare suitably welded together. As the conductor bars are configured asU-shaped bars, with each U-leg filling half of a rotor slot, thesquirrel-cage winding projects partly into the magnetic air gap (DE 2537 706 B1).

The rotor core of another known asynchronous machine is made of metalsheets provided with recesses for receiving conductor bars. Theconductor bars have ends associated to short-circuit rings which aresoldered to the ends of the conductor bars (DE 2 362 195 A1).

In order to achieve an asynchronous machine of great power and highoperating speed, a rotor construction is further known having a rotorcore made of metal sheets and associated to a pre-fabricated squirrelcage which is made of two half-cages with attached short-circuit ringswhich are welded or soldered together approximately in the area of halfthe length of the short-circuit rotor. Suitably, capping retaining ringsof high-strength, non-magnetic material are hereby additionally placedover the short-circuit rings (DE 197 29 432 C1).

SUMMARY OF THE INVENTION

Starting from a squirrel-cage rotor for an asynchronous induction motorhaving a rotor core made of massive steel and formed integrally with arotor shaft, wherein the rotor core is provided with slots extending inaxial direction, and conductor bars disposed in the slots and conformingto the slot cross section, wherein the conductor bars have ends, each ofwhich being short-circuited by a short-circuit ring by means of amaterial-interconnecting fit, the invention is based on the object toprovide a squirrel-cage rotor which allows operation at a power outputof the motor of more than 1 MW, even at rotation speeds of more than10,000 rpm and thus circumferential velocities of more than 200 m/sec,and yet is easy to manufacture.

This object is attained in accordance with the invention by providingthe slots with parallel or substantially parallel slot walls, and bysoldering the conductor bars over their entire length into the slots,with the conductor bars arranged flush with the surface of the rotorcore.

A squirrel-cage rotor configured in this manner is characterized by acage having in radial direction a small structural height. As aconsequence, the rotor shaft can have a greater diameter, when comparedto rotors that have a same outer diameter and a short-circuit cage ofgreater structural height, so that a stiffer rotor construction and thusless tendency to vibrate at high rotation speeds is realized. As theconductor bars are arranged flush with the surface of the rotor—forexample, by applying a material-removing process—the squirrel-cage rotorhas a smooth surface and thus very small friction losses. The solderingprocess, required to secure the conductor bars in the slots of the rotorcore, can easily be implemented. In order to introduce solder into thejoint area, it is recommended to provide the conductor bars with anelongate channel in the area confronting the slot base for introducingthe solder material before the conductor bars are placed into the slots.The channel may have a circular configuration for receiving a roundsolder wire. As an alternative, the rod-shaped or wire-shaped soldermaterial may initially be placed into the respective slot, andsubsequently the conductor bar with the channel are put over the soldermaterial.

The association of the short-circuit rings to the conductor bars,soldered into the slots of the rotor core, can be realized in accordancewith a further development of the invention by conically tapering therotor core and the conductor bars at the ends of the rotor core, i.e. inthe inactive zone of the short-circuit rings, and by soldering to thetapered region a short-circuit ring which on the inside is alsoconically tapered. In such a configuration, the short-circuit ringprojects only slightly beyond the diameter of the rotor core, wherebythe short-circuit ring—depending on the inclination of the conicaltaper—is connected across a large area with the conductor bars. Inaddition, this measure evens out the current distribution in the crosssection of the short-circuit ring, furthermore, differences in heatexpansion between rotor core and the short-circuit ring during thesoldering process can be compensated through axial displacement of theshort-circuit ring.

Instead of using a discrete short-circuit ring, it is also possible torealize the electrically required short circuiting in the area of theends of the conductor bars, which are shorter than the rotor core, byproviding two ring grooves whereby in the area of each of the ringgrooves two neighboring conductor bars are soldered together via aninserted intermediate piece.

BRIEF DESCRIPTION OF THE DRAWING

Two exemplified embodiments of the novel squirrel-cage rotor areillustrated in FIGS. 1 to 5, wherein

FIG. 1 shows a squirrel-cage rotor with conically tapered ends of theconductor bars at the ends of the rotor core,

FIG. 2 shows a detailed view of the association of conductor bars andshort-circuit ring according to FIG. 1,

FIG. 3 shows a cross sectional view of slots and conductor barsaccording to FIG. 1,

FIG. 4 shows a squirrel-cage rotor with short-circuit rings inset in thesurface area of the rotor core, and

FIG. 5 shows a cross section of the configuration of the short-circuitring according to FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the essential area of the squirrel-cage rotor of anasynchronous machine, whereby the lower part of the illustration depictsa plan view and the upper part of the illustration depicts alongitudinal section. The squirrel-cage rotor is made of massive steeland has a shaft 2 defined by the axis A and merging into a rotor core 3.The rotor core is selected with an outer diameter which is greater thanthe diameter of the shaft 12. Formed into the rotor core are axialslots, with webs 5 provided between the slots, wherein conductor bars 5are inserted in the slots and configured flush with the surface of therotor core by a finishing process.

Both end zones of the webs 5 and the conductor bars 4, placed in theslots of the rotor core, are conically tapered to thereby realizeconical regions 7 which taper toward the rotor axis. Placed over each ofboth regions 7 is a short-circuit ring 6. According to FIG. 2, the outerdiameter D_(R) of the short-circuit rings is selected slightly greaterthan the outer diameter D_(K) of the rotor core. The inclination of theconical taper is designated by the angle α, which is approximately 20°.

According to FIG. 3, the slots formed in the rotor core 3 are soconfigured as to include parallel slot walls 8 and 9 and to have aconcave slot base 10. The conductor bars placed into the slots conformto the slot cross section, and each of the conductor bars has in theconvex region, which complements the concave configuration of the slot,a channel 11 extending in longitudinal direction of the conductor barfor introduction of the solder material 12. As the rotor core is heated,this solder material is caused to melt so that the conductor bars 4 aresoldered in finished state in full contact in the slots.

The short-circuit rings 6, placed over the tapered ends of the conductorbars and the rotor core are also connected with the ends of theconductor bars and the slanted webs of the rotor core through amaterial-interconnecting fit, especially through soldering.

In the exemplified embodiment of a squirrel-cage rotor 20 according toFIGS. 4 and 5, the rotor core 21 is also provided with slots whichextend in longitudinal direction and between which webs 23 are formed.These slots are recessed into the surface of the rotor core. Conductorbars 23 are placed in these slots. Both ends of the slots have each anadditional ring-shaped groove 24 so that the webs 22 are shortened onboth ends. Placed in the regions between the webs 22 and the annulargrooves 24 are intermediate pieces 25 of a same material as theconductor bars, in particular copper. These intermediate pieces formtogether with the ends of the conductor bars both short-circuit rings.Intermediate pieces and ends of the conductor bars are also connected toone another through a soldering process in a material-interconnectingmanner. Hereby, the intermediate pieces according to FIG. 2 are providedwith lateral channels 26 for introduction of soldering material. Theconductor bars 23 are configured in a same manner and the conductor bars4 according to FIG. 2.

1. A squirrel-cage rotor for an asynchronous induction motor of greaterpower, comprising a rotor core made of massive steel and formedintegrally with a rotor shaft, said rotor core having a surface formedwith slots extending in axial direction and having parallel orsubstantially parallel slot walls; and conductor bars disposed in andsoldered along their entire length into the slots in one-to-onecorrespondence such as to extend flush with the surface of the rotorcore, wherein each of the conductor bars has a cross section conformingto a cross section of the corresponding slot and having opposite axialends; and a short-circuit assembly having two short-circuit rings, oneshort-circuit ring short-circuiting the one of the opposite axial endsof the conductor bars, and the other short-circuit ring short-circuitingthe other one of the opposite axial ends of the conductor bars by amaterial-interconnecting fit, wherein the rotor core has opposite ends,each said end of the rotor core and each said end of the conductor barsbeing conically tapered so that adjacent ends of the rotor core and theconductor bars define opposite tapered regions, wherein theshort-circuit rings are conically tapered on the inside and solderedonto the tapered regions.
 2. The squirrel-cage rotor of claim 1, whereinthe rotor core is provided in an end zone of each of the conductor barswith an annular groove, with the one axial ends of the conductor barsbeing soldered together via intermediate pieces placed into the annulargroove at one end zone of the rotor core, and the other axial ends ofthe conductor bars being soldered together via intermediate piecesplaced into the annular groove at the other end zone of the rotor core.3. The squirrel-cage rotor of claim 1, wherein each of the conductorbars is provided in an area facing a slot base with an elongate channelfor receiving solder material.
 4. The squirrel-cage rotor of claim 3,wherein the slot base of each slot has a concave configuration.
 5. Thesquirrel-cage rotor of claim 3, wherein the channel has a circularconfiguration for receiving solder material in the form of a roundsolder wire.